1. Field of the Invention
The present invention relates to a glass fiber for light transmission. More particularly, the present invention relates to an optical glass fiber having good lateral pressure characteristics and transmission properties.
2. Description of the Related Art
As shown in FIG. 1, a glass fiber for light transmission, namely an optical glass fiber has at least one coating layer around the fiber since it is difficult to maintain a mechanical strength and a transmission characteristics of a bare glass fiber in an as-drawn state. In general, the coating layer around the optical glass fiber 1 has a two-layer structure comprising an inner buffer layer 2 made of a comparatively soft material and an outer protective layer 3 made of a comparatively rigid material.
When a UV-curing resin is used as a resin for coating the optical glass fiber, a volume of the coating layer shrinks as the resin is cured after coating. Due to the volume shrinkage, the resin of the coating layer shrinks in a radial direction and a longitudinal direction of the glass fiber to generate strain in the glass fiber. When a resin having a large modulus is used for the formation of the protective layer, the strain in the glass fiber is considerable and light transmission loss increases. Such strain is one of problems which arise when a modulus of a coating material is increased. In particular, the strain generated by the coating layer is a big problem in maintaining lateral pressure characteristics since reduction of a diameter of an optical glass fiber is required to increase a density of a cable.
When an external pressure is applied to the optical glass fiber in a lateral direction, for example, when the optical glass fiber is wound around a bobbin, microbends are formed on the optical glass fiber and, as a result, light transmission loss increases. Such properties are referred to as "lateral pressure characteristics".